| VLDLy and VTG are two main yolk precursors, on the action of estrogen the precursors were synthesised and secreted in the liver and then transported to the follicular capillary by blood circulation, after that through the layers of the membrane structure of follicular and finally be endocytosised by OVR to form yolk. This study was divided into four parts.In trial 1, 48 Hy-line Brown layers(26wk)with similar body weight (BW) and egg production, were divided into 2 groups at random:CORT (hypodermic of abdomen on 7:00 and 19:00,2mg/kg.BW.Day) and control group (corn oil, hypodermic of abdomen on 7:00 and 19:00, 2mg/kg.BW.Day). Egg production, egg weight and feed intake were recorded every day. After 7 days CORT exposures, 10 eggs were sampled for the egg quality in the 8th day morning. Hens of each treatment were divided into fasting groups and feeding groups, access to water. 8 hens were weighed for each group, blood was drawn from a wing vein using a heparinized syringe and was stored at -20℃for further analysis after centrifugation. After hens were killed, preponderant follicle members was sampled, cooled down in liquid nitrogen immediately and stored at -80℃until analysis. The abdominal fat, preponderant foliclles and small yellow follicle (SYF) were harvested and weighed, and the numbers of follicles were recorded. The results showed that, fasting state, the expression of OVR, LPL, Occludin mRNA level of the follicle membrane increased significantly; Either fasting or feeding state, LHR, IGF-IR mRNA expression were not significant. It was suggested that CORT treatment caused ovarian developmental disorders, performance decreased was due to (the reduce of the concentration of yolk precursors) and the high expression of occludin on granular cell layer.In trial 2, 48 hens with similar BW and egg production, aged at 26 wk, were divided into 2 groups at random. Heat stress (30.5±0.1℃) and control group (23±0.1℃). After 7days treatment, 8 hens of each treatment were fasted for 12h and sampled as Part 1.The results showed that, The mRNA expression of Occludin was increased, While the mRNA expression of OVR, LPL, FSHR, LHR, IGF-IR in follicle membrane was no significant difference. Therefore heat stress affects yolk deposition may relation to the high expression of Occludin.In trial 3, 32 hens with similar BW and egg production, aged at 30 wk, were divided into 4 treatments at random. LC(standard diet+CORT), LO (standard diet+corn), HC (high energy diet+CORT), HO (high energy diet+corn). This trial was lasting 28 days. In the first 21 days, the standard diet groups fed standard diet, the high energy groups fed high-energy diet. At the last week, CORT groups (LC, HC) and control groups (LO, HO) treated as Part 1. Fasting 12h before sampling. Sampling as Part 1.The results showed that: standard diet state, CORT treatment significantly decreased egg production, there was no significant changes of feed intake; CORT treatment significantly decreased the weight of ovarian, rapid growth period follicles, while the weight of small yellow follicles was no significant changes. High-energy state, CORT treatment on feed intake and egg production had no significant effects, CORT treatment significantly reduced the number and weight rapid growth period follicles, while the weight of ovarian and small yellow follicular was no significant effect. Standard diet state, CORT treatment significantly decreased blood NEFA, VLDL, While plasma GLU, UA, TG, CHO were significant increased, significantly increased blood FSH, LH, INS levels, significantly reduced blood estrogen levels. High-energy state, CORT treatment significantly increased the UA and CHO levels, while NEFA, GLU, TG, VLDL had no significant effect; CORT treatment significantly increased the level of INS, while LH, FSH, estradiol had no significant effects. Standard diet state, CORT significantly increased the mRNA expression OVR, FSHR, Occludin, While LPL, LHR, ESR mRNA expression had no significant effects. High-energy state, CORT significantly increased the mRNA expression of OVR, ESR, while Occludin, FSHR, LHR, LPL mRNA expression was not significantly changed. Energy can alleviate performance degradation caused by CORT. This may relevant to high energy that raised the concentrations of yolk precursors and decreased the expression of Occludin mRNA on granulosa cells layer.In trial 4, 36 hens with similar BW and egg production, aged at 33 wk, were divided into 4 treatments at random. They were Control group, High-energy group,Estrogen treatment group and CORT treatment group. After treatment we draw blood as trial 1. Then ultracentrifugation plasma with density solutions, dynamic laser light scattering determination the diameter and distribution of VLDL particle. The results showed that CORT significant raised the diameter and decreased the distribution of VLDL. While high energy and estrogen had no significant effect to VLDL.
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